The Implications Of Medial And Lateral Co-Contractions Of Knee Muscle Pairs On Cartilage Health After Anterior Cruciate Ligament Reconstruction

Abstract

Anterior cruciate ligament (ACL) tears are very common, with over 120,000 individuals suffering these injuries every year in the United States. As ACL injuries often occur among active young adults, ACL reconstruction (ACLR) is recommended to restore knee stability and help patients return to pre-injury levels of activity. However, ACLR does not seem very effective in protecting knee cartilage from osteoarthritis (OA) development. Particularly, 50 – 70% of the individuals 5 – 15 years following ACLR develop knee OA. Thus, it is significant to assess the knee cartilage early after ACLR and investigate the potential mechanisms raising the risk of post-traumatic knee OA onset. Knee gait mechanics (kinetics and kinematics) have been investigated excessively after ACLR. Several studies have reported that altered knee loading early after ACLR is one of the primary mechanisms leading to knee OA. While the co-contraction indices (CCIs), indicative of co-contraction magnitude, of medial/lateral knee muscle pairs influence tibiofemoral loading, little is known about these indices early after ACLR and to what extent they impact cartilage integrity. Thus, the overall objective of this work is to understand the influences of medial/lateral knee muscle pairs co-contractions on the tibiofemoral cartilage health after ACLR. This dissertation aimed to compare the CCIs of medial and lateral knee muscle pairs in the involved and uninvolved limbs between sexes during gait 3 months after ACLR (Aim 1). Also, this work aimed to evaluate the association between medial compartment loading and the CCIs of knee muscle pairs early after ACLR (Aim 2), and to examine the relationship between knee muscle pairs CCIs and the biochemical structure of medial tibiofemoral cartilage (via assessing T2 relaxation time, indicative of collagen matrix degeneration) within the involved limb 3 and 24 months after ACLR (Aim 3). All aims were derived from a longitudinal cohort study, which had a gait biomechanical modeling and quantitative magnetic resonance imaging (qMRI). All participants had unilateral ACLR and underwent biomechanical gait analysis and sagittal MRI scan at 3, 6, and 24 months after ACLR. The key findings of Aim 1 suggest that individuals walk with higher CCIs of the lateral knee musculature in the involved limb (vs. uninvolved) 3 months after ACLR, and women (vs. men) walk with different neuromuscular adaptation by producing higher CCIs of muscle pairs incorporating the lateral gastrocnemius. Aim 2 indicates that individuals 3 months after ACLR exhibit higher CCIs of lateral knee musculature (vs. medial) during walking. This imbalance between the CCIs of medial and lateral knee muscle pairs in the involved limb is associated with medial compartment underloading of the tibiofemoral joint. Finally, Aim 3 reports that the alterations in CCIs of medial/lateral knee muscle pairs are not associated with the T2 relaxation times of any region in the medial tibiofemoral cartilage. This may suggest that walking with altered co-contractions of knee muscles might not be harmful to medial cartilage following ACLR. In summary, individuals early after ACLR walk with higher co-contraction of the lateral knee musculature (vs. medial) in the involved limb (vs. uninvolved). The same neuromuscular strategy has been seen among women only in the muscle pairs containing the lateral gastrocnemius. These early neuromuscular alterations after ACLR might contribute to aberrant medial tibiofemoral loading. Although no association has been found between these alterations and cartilage health, addressing the altered CCIs early after ACLR using neuromuscular intervention protocols might help to restore symmetrical knee loading. Thus, future work should investigate this question.